Gypsum Board and Gypsum Slurry Formed Using a Phosphorus Containing Compound

ABSTRACT

In general, the present invention is directed to the use of particular phosphorus containing compounds for making a gypsum board. The phosphorus containing compound may be a phosphite or a phosphate having a certain formula. In this regard, the present invention is directed to a slurry for making a gypsum board wherein the slurry includes such phosphorus containing compound. The present invention is also directed to a method of making a gypsum board from the slurry as well as a resulting gypsum board.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims filing benefit of U.S. Provisional PatentApplication Ser. No. 62/772,136 having a filing date of Nov. 28, 2018,and which is incorporated herein by reference in its entirety

BACKGROUND OF THE INVENTION

Gypsum board is commonly employed in drywall construction of interiorwalls and ceilings and also has other applications. Generally, thesegypsum boards are formed from a gypsum slurry including a mixture ofcalcined gypsum, water, and other conventional additives. The mixture iscast and allowed to set by reaction of the calcined gypsum with thewater. During the production process, free or unreacted water is removedin order to provide a relatively dry product. Typically, the amount ofwater necessary for forming the slurry is in excess of what is needed tocomplete the hydration reaction in order to provide a slurry havingsufficient fluidity to flow out of a mixer and onto a facing materialwhile also being able to be shaped to an appropriate width andthickness. In order to provide a stable board, once the gypsum has set,the excess water is removed through drying. However, the presence ofexcess water can create difficulties during processing. For instance,the excess water may extend the time in which the continuous gypsumsheet can be cut. Further, additional energy may be necessary to removethe excess water from the gypsum board. As a result, both limitationsmay result in an increase in cost and slower production.

As a result, there is a need to provide an improved method of making agypsum board.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a slurry formaking a gypsum board is disclosed. The slurry comprises stucco, water,and a phosphorus containing compound comprising a phosphite, a phosphatehaving the formula P(O)_(n)(X)_(m) wherein n is from 0 to 4, m is from 0to 6, the sum of n and m is from 3 to 6, and X is hydrogen, halogen,sulfur, or selenium, a salt thereof, or a mixture thereof.

In accordance with another embodiment of the present invention, a methodfor making a gypsum board is disclosed. The method comprises a step ofdepositing a slurry comprising stucco, water, and a phosphoruscontaining compound comprising a phosphite, a phosphate having theformula P(O)_(n)(X)_(m) wherein n is from 0 to 4, m is from 0 to 6, thesum of n and m is from 3 to 6, and X is hydrogen, halogen, sulfur, orselenium, a salt thereof, or a mixture thereof on a first facingmaterial. The method further comprises providing a second facingmaterial on the slurry and allowing the stucco to convert to calciumsulfate dihydrate.

In accordance with another embodiment of the present invention, a gypsumboard is disclosed. The gypsum board comprises gypsum and a phosphoruscontaining compound comprising a phosphite, a phosphate having theformula P(O)_(n)(X)_(m) wherein n is from 0 to 4, m is from 0 to 6, thesum of n and m is from 3 to 6, and X is hydrogen, halogen, sulfur, orselenium, a salt thereof, or a mixture thereof.

Other features and aspects of the present invention are set forth ingreater detail below.

DETAILED DESCRIPTION

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only and isnot intended as limiting the broader aspects of the present invention.

Generally speaking, the present invention is directed to a method ofmaking a gypsum slurry and a gypsum board using a certain phosphoruscontaining compound as defined herein. The present inventors havediscovered that such compound allows for an improved method ofmanufacture while still providing a board having desirable mechanicalproperties and characteristics.

As an example, by using the phosphorus containing compound as disclosedherein, in certain embodiments, the set time of the gypsum may beshortened which can in turn allow for an increase in production, forexample because of an increase in line speed. For example, by decreasingthe set time, the gypsum board may be cut sooner during the process.Furthermore, in other embodiments, the stiffening time may be extendedwhile maintaining a substantially similar set time. This may allow forthe mixer to remain relatively cleaner while also allow for the board tohave sufficient strength and hardness at the knife. In fact, as furtherindicated below, the board properties, such as nail pull resistance, mayeven be improved due to the use of the phosphorus containing compound.In addition to the properties mentioned above, the present inventorshave discovered that the phosphorus containing compound may also allowfor a substantial reduction, as further defined below, in the amount ofwater necessary during the process. In turn, such reduction may resultin less time necessary after cutting as well as heating in a heatingdevice, such as a kiln, for the removal of any excess free water. Inthis regard, with such reduction in time, this may also allow for anincrease in production in addition to a decrease in costs.

Generally, setting of a gypsum slurry is characterized by initial andfinal set times. Generally, the final set time corresponds to the timewhen a product or slurry has sufficiently hardened, for instance to becut in a clear manner such that it can be handled. It will be understoodby those skilled in the art that hydration reactions continue forextended periods even after the final set time has been reached.

Generally, setting may be referred to as the rate of hydration. The rateof hydration may be evaluated on the basis of the “Time to 50%Hydration.” For example, this time can be calculated by determining thetemperature increase caused by the hydration and then measuring theamount of time required to generate the temperature rise. The mid-pointin time has been found to correspond to the Time to 50% Hydration, as isknown to those skilled in the art. In this regard, with the use of thephosphorus containing compound, the Time to 50% Hydration of thecalcined gypsum may be about 10 minutes or less, such as about 9 minutesor less, such as about 8 minutes or less, such as about 7 minutes orless, such as about 6 minutes or less, such as about 5 minutes or less,such as about 4 minutes or less, such as 3 minutes or less, such as 2.5minutes or less. The Time to 50% Hydration may be about 0.5 minutes ormore, such as about 0.75 minutes or more, such as about 1 minute ormore, such as about 1.5 minutes or more, such as about 2 minutes ormore. Such times may be for a ⅝″ board. However, it should be understoodthat such times may also be for a board having another thickness asindicated herein. In addition, such times may be for a specific linespeed. In addition, this time may depend on certain other processparameters such as the type of board and slurry, board thickness, facingmaterial, dryer efficiency, and/or slurry additives.

The stiffening time may be about 5 minutes or less, such as about 4minutes or less, such as about 3 minutes or less, such as about 2minutes or less, such as about 1.5 minutes or less, such as about 1.4minutes or less, such as about 1.2 minutes or less, such as about 1.1minutes or less, such as about 1 minute or less, such as about 0.9minutes or less, such as about 0.8 minutes or less, such as about 0.7minutes or less, such as about 0.6 minutes or less, such as about 0.5minutes or less. The stiffening time may be about 0.1 minutes or more,such as about 0.2 minutes or more, such as about 0.3 minutes or more,such as about 0.4 minutes or more, such as about 0.5 minutes or more,such as about 0.6 minutes or more, such as about 0.7 minutes or more,such as about 0.8 minutes or more, such as about 0.9 minutes or more,such as about 1 minute or more. Such times may be for a ⅝″ board.However, it should be understood that such times may also be for a boardhaving another thickness as indicated herein.

In particular, the stiffening time may be extended in comparison to agypsum board formed without the phosphorus containing compound asdescribed herein. In particular, such stiffening time may be extended by5% or more, such as 10% or more, such as 15% or more, such as 20% ormore, such as 25% or more, such as 30% or more, such as 40% or more,such as 50% or more, such as 60% or more, such as 70% or more, such as80% or more. Such extension of the stiffening time may be 100% or less,such as 90% or less, such as 80% or less, such as 70% or less, such as60% or less, such as 50% or less, such as 40% or less. In addition, evenwith the extension of the stiffening time, the ¼ pound set time may notbe substantially affected.

For instance, the set time, as tested according to ASTM C266 using a ¼pound Gillmore needle may be about 10 minutes or less, such as about 8minutes or less, such as about 6 minutes or less, such as about 5minutes or less, such as about 4 minutes or less, such as about 3.5minutes or less, such as about 3.25 minutes or less, such as about 3minutes or less, such as about 2.9 minutes or less, such as about 2.8minutes or less, such as about 2.7 minutes or less, such as about 2.6minutes or less, such as about 2.5 minutes or less, such as about 2.4minutes or less. The set time may be about 0.5 minutes or more, such asabout 1 minute or more, such as about 1.5 minutes or more, such as about1.75 minutes or more, such as about 2 minutes or more, such as about 2.1minutes or more, such as about 2.2 minutes or more, such as about 2.3minutes or more, such as about 2.4 minutes or more, such as about 2.5minutes or more, such as about 3 minutes or more, such as about 3.5minutes or more, such as about 4 minutes or more, such as about 5minutes or more. Such times may be for a ⅝″ board. However, it should beunderstood that such times may also be for a board having anotherthickness as indicated herein.

In this regard, the set time may be within at least 1%, such as at least2%, such as at least 3%, such as at least 5%, such as at least 10%, suchas at least 15%, such as at least 20%, such as at least 25%, such as atleast 30%, such as at least 40%, such as at least 50% of the set time ofa process and slurry that does not utilize a phosphorus containingcompound as defined herein. Such percentages may be for a ⅝″ board.However, it should be understood that such percentages may also be for aboard having another thickness as indicated herein.

Furthermore, in some embodiments, the time from the deposition of theslurry to the cutter may be reduced when using the phosphorus containingcompound as disclosed herein. In particular, the time may be reduced byat least 1%, such as at least about 2%, such as at least 3%, such as atleast 5%, such as at least 10%, such as at least 15%, such as at least20% in comparison to the same process and slurry without the use of aphosphorus containing compound as defined herein. In addition, such timemay be reduced by 50% or less, such as 40% or less, such as 30% or less,such as 25% or less, such as 20% or less, such as 15% or less incomparison to the same process and slurry without the use of aphosphorus containing compound as defined herein. Such percentages maybe for a ⅝″ board. However, it should be understood that suchpercentages may also be for a board having another thickness asindicated herein. In general, the cutter may be positioned at least atthe point of about 80% hydration, such as at least about 85% hydration,such as at least about 90% hydration, such as at least about 95%hydration, such as at least about 97% hydration, such as at least about98% hydration for the gypsum.

In addition, when making a gypsum board with the phosphorus containingcompound as disclosed herein, the resulting board may exhibit desiredproperties, for instance even with an increase in stiffening time orfaster set time. In particular, these properties may be achieved eventhough the amount of water employed in the process may be reducedbecause of use of the phosphorus containing compound. For instance, withthe reduction in water, the gypsum may still set sufficiently to allowfor the desired properties to be realized.

The gypsum board may have a certain nail pull resistance, whichgenerally is a measure of the force required to pull a gypsum panel offof a wall by forcing a fastening nail through the panel. The valuesobtained from the nail pull test generally indicate the maximum stressachieved while the fastener head penetrates through the board surfaceand core. In certain embodiments, the nail pull resistance may beimproved due to the use of the phosphorus containing compound as definedherein. In this regard, the gypsum board exhibits a nail pull resistanceof at least about 25 lb_(f), such as at least about 30 pounds, such asat least about 35 lb_(f), such as at least about 40 lb_(f), such as atleast about 45 lb_(f), such as at least about 50 lb_(f), such as atleast about 55 lb_(f), such as at least about 60 lb_(f), such as atleast about 65 lb_(f), such as at least about 70 lb_(f), such as atleast about 75 lb_(f), such as at least about 77 lb_(f), such as atleast about 80 lb_(f), such as at least about 85 lb_(f), such as atleast about 90 lb_(f), such as at least about 95 lb_(f), such as atleast about 100 lb_(f) as determined according to ASTM C1396. The nailpull resistance may be about 150 lb_(f) or less, such as about 140lb_(f) or less, such as about 130 lb_(f) or less, such as about 120lb_(f) or less, such as about 110 lb_(f) or less, such as about 105lb_(f) or less, such as about 100 lb_(f) or less, such as about 95lb_(f) or less, such as about 90 lb_(f) or less, such as about 85 lb_(f)or less, such as about 80 lb_(f) or less as determined according to ASTMC1396. Such nail pull resistance may be based upon the thickness of thegypsum board. For instance, when conducting a test, such nail pullresistance values may vary depending on the thickness of the gypsumboard. As an example, the nail pull resistance values above may be for a⅝ inch board. However, it should be understood that instead of a ⅝ inchboard, such nail pull resistance values may be for any other thicknessgypsum board as mentioned herein.

The gypsum board may have a certain compressive strength. For instance,the compressive strength may be about 150 psi or more, such as about 200psi or more, such as about 250 psi or more, such as about 300 psi ormore, such as about 350 psi or more, such as about 375 psi or more, suchas about 400 psi or more, such as about 500 psi or more as testedaccording to ASTM C473. The compressive strength may be about 3000 psior less, such as about 2500 psi or less, such as about 2000 psi or less,such as about 1700 psi or less, such as about 1500 psi or less, such asabout 1300 psi or less, such as about 1100 psi or less, such as about1000 psi or less, such as about 900 psi or less, such as about 800 psior less, such as about 700 psi or less, such as about 600 psi or less,such as about 500 psi or less. Such compressive strength may be basedupon the thickness of the gypsum board. For instance, when conducting atest, such compressive strength values may vary depending on thethickness of the gypsum board. As an example, the compressive strengthvalues above may be for a ⅝ inch board. However, it should be understoodthat instead of a ⅝ inch board, such compressive strength values may befor any other thickness gypsum board as mentioned herein.

In addition, the gypsum board may have a core hardness of at least about8 lb_(f), such as at least about 10 pounds, such as at least about 11lb_(f), such as at least about 12 lb_(f), such as at least about 15lb_(f), such as at least about 18 lb_(f), such as at least about 20lb_(f) as determined according to ASTM C1396. The gypsum board may havea core hardness of 50 lb_(f) or less, such as about 40 lb_(f) or less,such as about 35 lb_(f) or less, such as about 30 lb_(f) or less, suchas about 25 lb_(f) or less, such as about 20 lb_(f) or less, such asabout 18 lb_(f) or less, such as about 15 lb_(f) or less as determinedaccording to ASTM C1396. In addition, the gypsum board may have an endhardness according to the aforementioned values. Further, the gypsumboard may have an edge hardness according to the aforementioned values.Such core hardness may be based upon the thickness of the gypsum board.For instance, when conducting a test, such core hardness values may varydepending on the thickness of the gypsum board. As an example, the corehardness values above may be for a ⅝ inch board. However, it should beunderstood that instead of a ⅝ inch board, such core hardness values maybe for any other thickness gypsum board as mentioned herein.

In addition, it may also be desired to have an effective bond betweenthe facing material and the gypsum core. Typically, a humidified bondanalysis is performed for 2 hours in a humidity chamber at 90° F. and90% humidity. In this test, after exposure, the facing material isremoved to determine how much remains on the gypsum board. The percentcoverage can be determined using various optical analytical techniques.In this regard, the facing material may cover less than 50%, such asless than 40%, such as less than 30%, such as less than 25%, such asless than 20%, such as less than 15%, such as less than 10%, such asless than 9%, such as less than 8% of the surface area of the gypsumcore upon conducting the test. Such percentage may be for a face of thegypsum board. Alternatively, such percentage may be for a back of thegypsum board. Further, such percentages may apply to the face and theback of the gypsum board. In addition, such values may be for an averageof at least 3 gypsum boards, such as at least 5 gypsum boards.

As indicated herein, the present invention utilizes a phosphoruscontaining compound for improving the process of making a gypsum slurryand a gypsum board as well as a resulting gypsum slurry and gypsumboard. In general, gypsum board is made from a gypsum slurry. Accordingto the present invention, the gypsum slurry includes at least stucco, aphosphorus containing compound as defined herein, and water.

In general, stucco may be referred to as calcined gypsum or calciumsulfate hemihydrate. The calcined gypsum may be from a natural source ora synthetic source and is thus not necessarily limited by the presentinvention. In addition to the stucco, the gypsum slurry may also containsome calcium sulfate dihydrate and/or calcium sulfate anhydrite. Ifcalcium sulfate dihydrate is present, the hemihydrate is present in anamount of at least 50 wt. %, such as at least 60 wt. %, such as at least70 wt. %, such as at least 80 wt. %, such as at least 85 wt. %, such asat least 90 wt. %, such as at least 95 wt. %, such as at least 98 wt. %,such as at least 99 wt. %, based on the weight of the calcium sulfatehemihydrate and the calcium sulfate dihydrate. Furthermore, the calcinedgypsum may be α-hemihydrate, β-hemihydrate, or a mixture thereof.

In addition to the stucco, the gypsum slurry may also contain otherhydraulic materials. These hydraulic materials may include calciumsulfate anhydrite, land plaster, cement, fly ash, or any combinationsthereof. When present, they may be utilized in an amount of 30 wt. % orless, such as 25 wt. % or less, such as 20 wt. % or less, such as 15 wt.% or less, such as 10 wt. % or less, such as 8 wt. % or less, such as 5wt. % or less based on the total content of the hydraulic material.

The phosphorus containing compound may be a phosphite, a phosphatehaving the formula P(O)_(n)(X)_(m) wherein n is from 0 to 4, m is from 0to 6, the sum of n and m is from 3 to 6, and X is hydrogen, halogen,sulfur, or selenium, a salt thereof, or a mixture thereof. In oneembodiment, the phosphorus containing compound comprises a phosphite ora salt thereof. In another embodiment, the phosphorus containingcompound comprises a phosphate having the formula P(O)_(n)(X)_(m)wherein n is from 0 to 4, m is from 0 to 6, the sum of n and m is from 3to 6, and X is hydrogen, halogen, sulfur, or selenium, or a saltthereof. In a further embodiment, the phosphorus containing compoundcomprises a combination of a phosphite or a salt thereof and a phosphatehaving the formula P(O)_(n)(X)_(m) wherein n is from 0 to 4, m is from 0to 6, the sum of n and m is from 3 to 6, and X is hydrogen, halogen,sulfur, or selenium, or a salt thereof.

As indicated above, the phosphorus containing compound may be aphosphate having the formula P(O)_(n)(X)_(m) wherein n is from 0 to 4, mis from 0 to 6, the sum of n and m is from 3 to 6, and X is hydrogen,halogen, sulfur, or selenium, or a salt thereof. In this regard X may behydrogen, halogen, or sulfur. For instance, X may be halogen or sulfur.In one embodiment, X may be sulfur. In a further embodiment, X may beselenium. In another embodiment, X may be hydrogen. In anotherembodiment, X may be halogen. For instance, the halogen may be fluorine(or fluoro), chlorine (or chloro), bromine (or bromo), iodine (or iodo),or any combination thereof. For instance, in one embodiment, the halogenmay be fluorine (or fluoro). It should be noted that when m is greaterthan 1, each X may be independent of another X. That is, each X may beidentical or alternatively, one X may be different from another X.

In addition, as indicated above, n is from 0 to 4, such as from 1 to 4,such as from 2 to 4, such as from 2 to 3. Thus, n may be at least 0,such as at least 1, such as at least 2, such as at least 3 to 4 or less,such as 3 or less, such as 2 or less, such as 1 or less. Thus, n may be0. Further, n may be 1. In another embodiment, n may be 2. In a furtherembodiment, n may be 3. In another further embodiment, n may be 4.

Also, as indicated above, m is from 0 to 6, such as from 1 to 6, such asfrom 1 to 5, such as from 1 to 4, such as from 1 to 3, such as from 1 to2 or 2 to 3. Thus, m may be at least 0, such as at least 1, such as atleast 2, such as at least 3, such as at least 4, such as at least 5 to 6or less, such as 5 or less, such as 4 or less, such as 3 or less, suchas 2 or less, such as 1 or less. In this regard, m may be 1. In anotherembodiment, m may be 2. In a further embodiment, m may be 3. In anotherfurther embodiment, m may be 4. In one embodiment, m may be 5. Finally,in a further embodiment, m may be 6.

In addition, as indicated above, the sum of n and m may be from 3 to 6.In this regard, the sum of n and m may be at least 3, such as at least4, such as at least 5 to 6 or less, such as 5 or less, such as 4 orless. In one embodiment, the sum of n and m may be 3. In anotherembodiment, the sum of n and m may be 4. In a further embodiment, thesum of n and m may be 5. In another further embodiment, the sum of n andm may be 6.

In one particular embodiment, X may be halogen, such as fluorine(fluoro), n may be 3, and m may be 1. In another particular embodiment,X may be halogen, such as fluorine (fluoro), n may be 2, and m may be 2.In this regard, when X is halogen, the phosphorus containing compoundmay be referred to as a halophosphate.

When the phosphorus containing compound comprises a halophosphate, thehalo may be any halogen atom suitable for the present invention. In thisregard, the halogen may be fluorine (or fluoro), chlorine (or chloro),bromine (or bromo), iodine (or iodo), or any combination thereof. Forinstance, in one embodiment, the halogen may be fluorine (or fluoro)such that the halophosphate is a fluorophosphate. In another embodiment,the halogen may be chlorine (or chloro) such that the halophosphate is achlorophosphate.

Further, the halophosphate may comprise any number of halogen atoms. Forinstance, the halophosphate may include at least 1 halogen atom, such asat least 2 halogen atoms, such as at least 3 halogen atoms, such as atleast 4 halogen atoms, such as at least 5 halogen atoms, such as atleast 6 halogen atoms. In this regard, the halophosphate may be amonohalophosphate, a dihalophosphate, a trihalophosphate, atetrahalophosphate, a pentahalophosphate, a hexahalophosphate, or anymixture thereof. In one embodiment, the halophosphate includes amonohalophosphate. In another embodiment, the halophosphate includes adihalophosphate.

As indicated above, the halogen may be fluorine. In this regard, thehalophosphate may be a fluorophosphate. In particular, thefluorophosphate may be a monofluorophosphate, a difluorophosphate, atrifluorophosphate, a tetrafluorophosphate, a pentafluorophosphate, ahexafluorophosphate, or any mixture thereof. In one embodiment, thefluorophosphate may include a monofluorophosphate. In anotherembodiment, the fluorophosphate may include a difluorophosphate.

As also indicated above, X may be a hydrogen. In this regard, m maybe 1. In one embodiment, m may be 2 such that the phosphate is adihydrogen phosphate. In a particular embodiment, the compound may be abis(dihydrogen phosphate). In another particular embodiment, thecompound may be a tris(dihydrogen phosphate).

As indicated above, the phosphorus containing compound may be aphosphite. For instance, the phosphite may be an anion having thegeneral formula [HPO₃]²⁻. In this regard, the phosphite may be a salt ofphosphorus acid. In one embodiment, the phosphite may have the formulaof the aforementioned phosphate wherein X is H. The remaining parametersof such formula may be the same as defined above and herein with respectto the phosphate. For instance, in the above formula, n may be 3 and mmay be 1.

Furthermore, the phosphorus containing compound may be a salt. In thisregard, the phosphorus containing compound may include ammonium, ametal, or a combination thereof. In one embodiment, the phosphoruscontaining compound includes ammonium. In another embodiment, thephosphorus containing compound includes a metal.

When the phosphorus containing compound includes a metal, the metal maybe any employed in the art. For instance, the metal may be an alkalimetal, an alkaline earth metal, a transition metal, or a combinationthereof. In one embodiment, the metal may be an alkali metal. Forinstance, the alkali metal may be lithium, sodium, potassium, or acombination thereof. In one particular embodiment, the alkali metal maybe sodium, potassium, or a combination thereof. In another particularembodiment, the alkali metal may include sodium.

In another embodiment, the metal may be an alkaline earth metal. Forinstance, the alkaline earth metal may be beryllium, magnesium, calcium,strontium, barium, or a combination thereof. In one particularembodiment, the alkaline earth metal may be magnesium, calcium, or acombination thereof.

In a further embodiment, the metal may be a transition metal. Forinstance, the transition metal may be manganese, iron, cobalt, nickel,copper, zinc, titanium, chromium, platinum, gold, molybdenum, palladium,silver, tantalum, tungsten, etc., or a combination thereof.

In addition to alkali metals, alkaline earth metals, and transitionmetals, other metals may also be employed. For instance, the metal maybe aluminum, indium, tin, bismuth, etc., or a combination thereof.

Furthermore, one mole of metal may be present. Alternatively, in oneembodiment, two moles of metal may be present. As an example, the metalmay simply be sodium. Alternatively, the metal may be disodium. In thisregard, the number of moles of metal may depend on the charge of theanion. Thus, if the anion has a charge of −6, six moles of sodium may berequired.

The phosphorus containing compound may be present in the gypsum slurryin an amount of 0.001 wt. % or more, such as 0.01 wt. % or more, such as0.02 wt. % or more, such as 0.05 wt. % or more, such as 0.1 wt. % ormore, such as 0.15 wt. % or more, such as 0.2 wt. % or more, such as0.25 wt. % or more, such as 0.3 wt. % or more, such as 0.5 wt. % or morebased on the weight of the stucco. The phosphorus containing compoundmay be present in an amount of 10 wt. % or less, such as 7 wt. % orless, such as 5 wt. % or less, such as 4 wt. % or less, such as 3 wt. %or less, such as 2.5 wt. % or less, such as 2 wt. % or less, such as 1.8wt. % or less, such as 1.5 wt. % or less, such as 1 wt. % or less, suchas 0.8 wt. % or less, such as 0.6 wt. % or less, such as 0.5 wt. % orless, such as 0.4 wt. % or less, such as 0.35 wt. % or less, such as 0.2wt. % or less based on the weight of the stucco.

As indicated above, the gypsum slurry may also include water. Water maybe employed for fluidity and also for rehydration of the gypsum to allowfor setting. The amount of water utilized is not necessarily limited bythe present invention. However, it should be understood that asindicated herein, the utilization of the phosphorus containing compoundmay allow for a reduction in the amount of water required in comparisonto a process that may not utilize the phosphorus containing compound.

In addition, the weight ratio of the water to the stucco may be 0.1 ormore, such as 0.2 or more, such as 0.3 or more, such as 0.4 or more,such as 0.5 or more. The water to stucco weight ratio may be 4 or less,such as 3.5 or less, such as 3 or less, such as 2.5 or less, such as 2or less, such as 1.7 or less, such as 1.5 or less, such as 1.4 or less,such as 1.3 or less, such as 1.2 or less, such as 1.1 or less, such as 1or less, such as 0.9 or less, such as 0.85 or less, such as 0.8 or less,such as 0.75 or less, such as 0.7 or less, such as 0.6 or less, such as0.5 or less, such as 0.4 or less, such as 0.35 or less, such as 0.3 orless, such as 0.25 or less, such as 0.2 or less. With the use of thephosphorus containing compound as disclosed herein, the amount of waterrequired may be less than other conventional processes. For instance,the gypsum slurry may require a reduction in the amount of waternecessary by at least 5 wt. %, such as at least 8 wt. %, such as atleast 10 wt. %, such as at least 15 wt. %, such as at least 20 wt. %,such as at least 25 wt. % and less than 50 wt. %, such as less than 40wt. %, such as less than 30 wt. %, such as less than 25 wt. %, such asless than 20 wt. %, in comparison to a gypsum slurry that does notcontain a phosphorus containing compound as disclosed herein. Even witha reduction in water, the slurry may exhibit a similar slump, stiffeningtime, and/or set time in comparison to a slurry that does not contain aphosphorus containing compound as disclosed herein. For instance, suchproperty of the slurry may be within 1%, such as within 3%, such aswithin 5%, such as within 10%, such as within 15%, such as within 20% ofthe property of slurry that does not contain a phosphorus containingcompound as disclosed herein.

In addition to the stucco, the phosphorus containing compound, and thewater, the gypsum slurry may also include any other conventionaladditives as known in the art. In this regard, such additives are notnecessarily limited by the present invention. For instance, theadditives may include dispersants, foam or foaming agents includingaqueous foam (e.g. sulfates), set accelerators (e.g., BMA, land plaster,sulfate salts, etc.), set retarders, binders, biocides (such asbactericides and/or fungicides), adhesives, pH adjusters, thickeners(e.g., silica fume, Portland cement, fly ash, clay, celluloses, highmolecular weight polymers, etc.), leveling agents, non-leveling agents,starches (such as pregelatinized starch, non-pregelatinized starch,and/or an acid modified starch), colorants, fire retardants or additives(e.g., silica, silicates, expandable materials such as vermiculite,perlite, etc.), water repellants, fillers (e.g., glass fibers), waxes,secondary phosphates (e.g., condensed phosphates or orthophosphatesincluding trimetaphosphates, polyphosphates, and/or cyclophosphates,etc.), polymers (natural polymers, synthetic polymers), mixturesthereof, etc. In general, it should be understood that the types andamounts of such additives are not necessarily limited by the presentinvention.

In general, each additive may be present in the gypsum slurry in anamount of 0.0001 wt. % or more, such as 0.001 wt. % or more, such as0.01 wt. % or more, such as 0.02 wt. % or more, such as 0.05 wt. % ormore, such as 0.1 wt. % or more, such as 0.15 wt. % or more, such as 0.2wt. % or more, such as 0.25 wt. % or more, such as 0.3 wt. % or more,such as 0.5 wt. % or more, such as 1 wt. % or more, such as 2 wt. % ormore based on the weight of the stucco. The additive may be present inan amount of 20 wt. % or less, such as 15 wt. % or less, 10 wt. % orless, such as 7 wt. % or less, such as 5 wt. % or less, such as 4 wt. %or less, such as 3 wt. % or less, such as 2.5 wt. % or less, such as 2wt. % or less, such as 1.8 wt. % or less, such as 1.5 wt. % or less,such as 1 wt. % or less, such as 0.8 wt. % or less, such as 0.6 wt. % orless, such as 0.5 wt. % or less, such as 0.4 wt. % or less, such as 0.35wt. % or less, such as 0.2 wt. % or less based on the weight of thestucco.

As indicated above, the additives may include at least one dispersant.The dispersant is not necessarily limited and may include any that canbe utilized within the gypsum slurry and the phosphorus containingcompound disclosed herein. The dispersant may include carboxylates,sulfates, sulfonates, mixtures thereof, etc. For instance, in oneembodiment, the dispersant may include a sulfate.

In another embodiment, the dispersant may include a carboxylate, such asa carboxylate ether and in particular a polycarboxylate ether or acarboxylate ester and in particular a polycarboxylate ester. In general,the carboxylate or polycarboxylate may be derived from an acrylic acidor a salt thereof, such as a methacrylic acid or a salt thereof. Inaddition, the polycarboxylate ether copolymer optionally has additionalstructural groups in copolymerized form. In this case, the additionalstructural groups may include styrenes, acrylamides, hydrophobiccompounds, ester repeating unit, polypropylene oxide and polypropyleneoxide/polyethylene oxide units. In addition, any comb-branchedpolycarboxylate dispersant may be useful in the slurry. In particular,the polycarboxylate dispersant may be one having polyether side chains.The polycarboxylate ester in some embodiments may be prepared bypolymerization of a monomer mixture containing a carboxylic acid monomeras the main component. In other embodiments, it is advantageous if theformula (I) represents a polyether containing alkyl or vinyl groups. Anaspect of many polycarboxylate esters is their anti-foaming, defoamingand/or surface active properties. Therefore in some embodiments wherethe dispersant component is such a polycarboxylate ester, the dispersantcomponent can provide antifoaming and surfactant effects in addition totheir dispersing effect. In some embodiments, the monomer mixtureincludes an (alkoxy)polyalkylene glycol mono(meth)acrylate monomer ofthe general formula (II):

In particular, the dispersant may include a sulfonate, such as anaphthalene sulfonate, a lignosulfonate, or a mixture thereof. Inparticular, the sulfonate may be a polynaphthalene sulfonate. Thenaphthalene sulfonate may have an average molecular weight of at leastabout 1000 g/mol, such as at least about 2000 g/mol, such as at leastabout 3000 g/mol, such as at least about 5000 g/mol, such as about atleast about g/mol to about 40000 g/mol or less, such as about 30000g/mol or less, such as about 25000 g/mol or less, such as about 20000g/mol or less, such as about 15000 g/mol or less, such as about 10000g/mol or less, such as about 8000 g/mol or less.

In this regard, the dispersant may include a sulfonate, apolycarboxylate ether, a polycarboxylate ester, or a mixture thereof.

As indicated above, the additives may include at least one accelerator.The accelerator is not necessarily limited and may include any that canbe utilized within the gypsum slurry and the phosphorus containingcompound disclosed herein. The accelerator may include ground orunground gypsum such as from a ball mill accelerator, land plaster,sulfate salts, etc., as well as a mixture thereof. In one embodiment,the accelerator may include at least a ball mill accelerator (BMA).

The slurry may also have a certain volume content of air. For instance,1% or more, such as 5% or more, such as 10% or more, such as 20% ormore, such as 25% or more, such as 30% or more of the slurry volume maybe air. In addition, 80% or less, such as 70% or less, such as 60% orless, such as 50% or less, such as 40% or less of the slurry volume maybe air. The volume may be formed by employing an aqueous foam.

The slurry may also have a particular slump as defined herein. Forinstance, the slump may be 5 inches or more, such as 6 inches or more,such as 6.5 inches or more, such as 6.75 inches or more, such as 7inches or more, such as 7.125 inches or more, such as 7.25 inches ormore, such as 7.5 inches or more, such as 7.75 inches or more, such as 8inches or more, such as 8.125 inches or more, such as 8.25 inches ormore. The slump may be 10 inches or less, such as 9 inches or less, suchas 8.5 inches or less, such as 8.25 inches or less, such as 8 inches orless, such as 7.75 inches or less, such as 7.5 inches or less, such as7.25 inches or less. In general, the greater the slump, the greater thefluidity of the gypsum slurry.

The present invention is also directed to a method of making a gypsumslurry. The method includes a step of combining stucco, water, and aphosphorus containing compound as defined herein. The method may alsoinclude combining any of the other aforementioned components mentionedabove with respect to the gypsum slurry.

The manner in which the components are combined is not necessarilylimited. For instance, the gypsum slurry can be made using any method ordevice generally known in the art. In particular, the components of theslurry can be mixed or combined using any method or device generallyknown in the art. For instance, the components of the gypsum slurry maybe combined in any type of device, such as a mixer and in particular apin mixer. In this regard, the manner in which the phosphorus containingcompound is incorporated into the gypsum slurry is not necessarilylimited by the present invention. For instance, the phosphoruscontaining compound may be provided prior to a mixing device, directlyinto a mixing device, and/or after the mixing device. Further, whenprovided after the mixing device, the phosphorus containing compound maybe provided to a canister or boot or by using a secondary mixer. Inaddition, the phosphorus containing compound may be provided alone, aspart of a mixture, or in a solution. For instance, it may be provided oradded to a mixing device or another compound either alone or as part ofa mixture. For instance, the phosphorus containing compound may becombined directly with another component of the gypsum slurry. Inaddition, the phosphorus containing compound may be delivered as asolid, as a dispersion/solution, or a combination thereof.

In addition to a method of making a gypsum slurry, the present inventionis also directed to a method of making a gypsum board. The method mayinclude the aforementioned step of combining stucco, water, and aphosphorus containing compound as defined herein. In addition, themethod may also include combining any of the other aforementionedcomponents mentioned above with respect to the gypsum slurry. Thecomponents of the gypsum slurry may be combined in any type of device,such as a mixer and in particular a pin mixer.

Once the gypsum slurry is prepared, the method may comprise a step ofdepositing the gypsum slurry onto a first facing material. The firstfacing material may be conveyed on a conveyor system (i.e., a continuoussystem for continuous manufacture of gypsum board). Next, a secondfacing material is provided on top of the gypsum slurry such that thegypsum slurry is sandwiched between the facing materials in order toform the gypsum board.

The facing material may be any facing material as generally employed inthe art. For instance, the facing material may be a paper facingmaterial, a fibrous (e.g., glass fiber) mat facing material, or apolymeric facing material. In general, the first facing material and thesecond facing material may be the same type of material. Alternatively,the first facing material may be one type of material while the secondfacing material may be a different type of material.

In one embodiment, the facing material may include a paper facingmaterial. For instance, both the first and second facing materials maybe a paper facing material. Alternatively, in another embodiment, thefacing material may be a glass mat facing material. For instance, boththe first and second facing materials may be a glass mat facingmaterial. In a further embodiment, the facing material may be apolymeric facing material. For instance, both the first and secondfacing materials may be a polymeric facing material.

After deposition, the calcium sulfate hemihydrate reacts with the waterto convert the calcium sulfate hemihydrate into a matrix of calciumsulfate dihydrate. Such reaction may allow for the gypsum to set andbecome firm thereby allowing for the boards to be cut at the desiredlength. In this regard, the method may comprise a step of reactingcalcium sulfate hemihydrate with water to form calcium sulfate dihydrateor allowing the calcium sulfate hemihydrate to convert to calciumsulfate dihydrate. In this regard, the method may allow for the slurryto set to form a gypsum board. In addition, during this process, themethod may allow for dewatering of the gypsum slurry, in particulardewatering any free water instead of combined water of the gypsumslurry. Such dewatering may occur prior to the removal of any freemoisture or water in a heating device after a cutting step. Thereafter,the method may also comprise a step of cutting a continuous gypsum sheetinto a gypsum board. Then, after the cutting step, the method maycomprise a step of supplying the gypsum board to a heating device. Forinstance, such heating device may be a kiln and may allow for removal ofany free water. The temperature and time required for heating in suchheating device are not necessarily limited by the present invention.

In this regard, the present invention is also directed to a gypsumboard. The gypsum board includes a gypsum core sandwiched between twofacing materials. The gypsum board may comprise calcium sulfatedihydrate and a phosphorus containing compound as defined herein or asalt thereof. For instance, the phosphorus containing compound maycomprise a phosphite, a phosphate having the formula P(O)_(n)(X)_(m)wherein n is from 0 to 4, m is from 0 to 6, the sum of n and m is from 3to 6, and X is hydrogen, halogen, sulfur, or selenium, a salt thereof,or a mixture thereof. In particular, the phosphorus containing compoundmay comprise a phosphate having the formula P(O)_(n)(X)_(m) wherein n isfrom 0 to 4, m is from 0 to 6, the sum of n and m is from 3 to 6, and Xis hydrogen, halogen, sulfur, or selenium, a salt thereof, or a mixturethereof.

In one embodiment, the phosphorus containing compound may comprise aphosphite or a salt thereof. In another further embodiment, thephosphorus containing compound may comprise a salt of a phosphite. Forexample, the phosphite itself may be a phosphite anion.

In a further embodiment, the phosphorus containing compound may comprisea phosphate having the formula P(O)_(n)(X)_(m) wherein n is from 0 to 4,m is from 0 to 6, the sum of n and m is from 3 to 6, and X is hydrogen,halogen, sulfur, or selenium, or a salt thereof. In another furtherembodiment, the phosphorus containing compound may comprise a salt of aphosphate having the formula P(O)_(n)(X)_(m) wherein n is from 0 to 4, mis from 0 to 6, the sum of n and m is from 3 to 6, and X is a halogen.For example, the phosphate itself may be a phosphate anion. In an evenfurther embodiment, the phosphorus containing compound may comprise acombination of a phosphate having the formula P(O)_(n)(X)_(m) wherein nis from 0 to 4, m is from 0 to 6, the sum of n and m is from 3 to 6, andX is a halogen or sulfur or a salt thereof.

As an example, the phosphorus containing compound may be sodiummonofluorophosphate. The salt includes when the components are presentas ions of such compound or disassociated. For instance, the gypsumboard may comprise sodium and monofluorophosphate, which may not becomplexed but instead may be uncomplexed or disassociated. Additionally,when disassociated, the gypsum board may include one of the ions or bothof the ions. Using the example of sodium monofluorophosphate, the gypsumboard may include sodium, monofluorophosphate, or both sodium andmonofluorophosphate. In one embodiment, the phosphate component, such asthe halofluorophosphate (e.g., monofluorophosphate), may complex withanother cation or metal.

The phosphorus containing compound may be present in an amount of 0.001wt. % or more, such as 0.01 wt. % or more, such as 0.02 wt. % or more,such as 0.05 wt. % or more, such as 0.1 wt. % or more, such as 0.15 wt.% or more, such as 0.2 wt. % or more, such as 0.25 wt. % or more, suchas 0.3 wt. % or more, such as 0.5 wt. % or more based on the weight ofthe gypsum board. The phosphorus containing compound may be present inan amount of 10 wt. % or less, such as 7 wt. % or less, such as 5 wt. %or less, such as 4 wt. % or less, such as 3 wt. % or less, such as 2.5wt. % or less, such as 2 wt. % or less, such as 1.8 wt. % or less, suchas 1.5 wt. % or less, such as 1 wt. % or less, such as 0.8 wt. % orless, such as 0.6 wt. % or less, such as 0.5 wt. % or less, such as 0.4wt. % or less, such as 0.35 wt. % or less, such as 0.2 wt. % or lessbased on the weight of the gypsum board. Alternatively, rather than theweight of the board, such compound may be present in such amounts basedon the weight of the calcium sulfate dihydrate.

The phosphorus containing compound may be present in an amount of 0.001lbs/MSF or more, such as 0.01 lbs/MSF or more, such as 0.05 lbs/MSF ormore, such as 0.1 lbs/MSF or more, such as 0.2 lbs/MSF or more, such as0.25 lbs/MSF or more, such as 0.5 lbs/MSF or more, such as 0.75 lbs/MSFor more, such as 1 lb/MSF or more, such as 1.5 lbs/MSF or more, such as2 lbs/MSF or more, such as 2.5 lbs/MSF or more, such as 3 lbs/MSF ormore, such as 4 lbs/MSF or more. The phosphorus containing compound maybe present in an amount of 150 lbs/MSF or less, such as 100 lbs/MSF orless, such as 50 lbs/MSF or less, such as 25 lbs/MSF or less, such as 15lbs/MSF or less, such as 10 lbs/MSF or less, such as 5 lbs/MSF or less,such as 4 lbs/MSF or less, such as 3 lbs/MSF or less, such as 2.5lbs/MSF or less, such as 2 lbs/MSF or less, such as 1.5 lbs/MSF or less,such as 1 lbs/MSF or less.

The thickness of the gypsum board is not necessarily limited and may befrom about 0.25 inches to about 1 inch. For instance, the thickness maybe at least ¼ inches, such as at least 5/16 inches, such as at least ⅜inches, such as at least 4/10 inches, such as at least ½ inches, such asat least ⅝ inches, such as at least ¾ inches, such as at least 1 inch.In this regard, the thickness may be about any one of the aforementionedvalues. For instance, the thickness may be about ¼ inches.Alternatively, the thickness may be about ⅜ inches. In anotherembodiment, the thickness may be about ½ inches. In a furtherembodiment, the thickness may be about ⅝ inches. In another furtherembodiment, thickness may be about 1 inch. With regard to the thickness,the term “about” may be defined as within 10%, such as within 5%, suchas within 4%, such as within 3%, such as within 2%, such as within 1%.

The gypsum board may also have a certain void volume. In general, thevoid volume may refer to the volume of the board occupied by air and notany material. The void volume of the gypsum board may be 5% or more,such as 10% or more, such as 20% or more, such as 25% or more, such as30% or more, such as 40% or more, such as 50% or more. The void volumemay be 90% or less, such as 80% or less, such as 70% or less, such as60% or less, such as 50% or less, such as 40% or less, such as 30% orless.

In this regard, the gypsum board may have a density of about 5 pcf ormore, such as about 10 pcf or more, such as about 15 pcf or more, suchas about 20 pcf or more. The board may have a density of about 60 pcf orless, such as about 50 pcf or less, such as about 40 pcf or less, suchas about 35 pcf or less, such as about 33 pcf or less, such as about 30pcf or less, such as about 28 pcf or less, such as about 25 pcf or less,such as about 23 pcf or less, such as about 20 pcf or less.

In addition, the board weight of the gypsum board is not necessarilylimited. For instance, the gypsum board may have a board weight of 500lbs/MSF or more, such as about 600 lbs/MSF or more, such as about 700lbs/MSF or more, such as about 800 lbs/MSF or more, such as about 900lbs/MSF or more, such as about 1000 lbs/MSF or more, such as about 1100lbs/MSF or more, such as about 1200 lbs/MSF or more, such as about 1300lbs/MSF or more, such as about 1400 lbs/MSF or more, such as about 1500lbs/MSF or more, such as about 2000 lbs/MSF or more, such as about 2500lbs/MSF or more, such as about 3000 lbs/MSF or more. The board weightmay be about 5000 lbs/MSF or less, such as about 4500 lbs/MSF or less,such as about 4000 lbs/MSF or less, such as about 3500 lbs/MSF or less,such as about 3000 lbs/MSF or less, such as about 2500 lbs/MSF or less,such as about 2000 lbs/MSF or less, such as about 1800 lbs/MSF or less,such as about 1600 lbs/MSF or less, such as about 1500 lbs/MSF or less,such as about 1400 lbs/MSF or less, such as about 1300 lbs/MSF or less,such as about 1200 lbs/MSF or less. Such board weight may be a dry boardweight such as after the board leaves the heating device (e.g., kiln).

EXAMPLES Test Methods

Stiffening time: The stiffening time is the amount of time for a linedrawn through the gypsum slurry to remain visible (e.g., unhealed). Inparticular, a paper clip tip was used to draw a line through the slurry.The stiffening time was determined as the time at which the lineremained visible or it no longer healed.

Set time: The set time is the time between the initial and final settimes as determined according to ASTM C266 using a ¼ lb Gilmore needle.

Slump test: The test is conducted after dipping a brass cylinder havinga wall thickness of about 0.07 inches, a height of about 4 inches, andan inner diameter of about 2 inches into a low-viscosity lubricating oilbath. The cylinder was removed and excess oil was drained off thesurfaces of the cylinder. The cylinder then was placed upright onto acenter portion of a clean (i.e., no scratches), dry glass plate havingthe following dimensions: about 10 inches in length, about 10 inches inwidth, and about 0.1875 inch thick. The gypsum slurry, which wasobtained from about 12 inches down the line from the mixer boot, wasimmediately poured into the cylinder such that the cylinder wascompletely filled with a slight excess. The scoop can be a clean metalor plastic scoop of convenient size or can be formed from disposablegypsum board paper. The excess was screed off to a level with the top ofthe cylinder without dropping any of the slurry onto the surface of theglass plate. Immediately, and at least within about 10 seconds ofremoving excess slurry, the cylinder was raised vertically with a smoothand uniform motion at a moderate (not rapid) speed, and the slurrycontained within the cylinder was allowed to slump to a circular pattyonto the surface of the glass plate. After the slurry had solidified,the glass plate was turned over and the diameter of the slump in contactwith the glass plate was measured to the nearest ⅛ inch. In particular,the average of two measurements was reported wherein the measurementsare taken at right angles to each other.

Nail pull: The nail pull is determined in accordance with ASTM C1396.For these tests, the gypsum board were condition at 70° F. and 50%relative humidity for at least 6 hours.

Example 1

Gypsum boards were made with a formulation including stucco, water(i.e., water to stucco ratio of 0.9), foam, and ball mill accelerator.For the control samples, Plast-L (i.e., mixture of degraded polyamidessalified with sodium in aqueous solution and a chemically modifiednatural polymer in aqueous solution) was used as the set retarder. Inthe inventive samples, about 1.0 g (0.14 wt. % based on stucco) ofsodium monofluorophosphate was provided to the gypsum slurry. Theresults are shown in the table below:

Core Stiffening Board Compressive Sample time Set time Weight Nail PullStrength Description No. (s) (min:s) (lbs/MSF) (lb_(f)) (psi) Control CS1 37 2:26 1337 75 329 (1.0 g 10% Plast-L) CS 2 35 2:36 1278 66 — CS 3 372:47 1186 50 — CS 4 35 2:25 1436 84 — 1.0 g Sodium S 1 36 2:30 1320 73 —Monofluorophosphate S 2 39 2:40 1357 79 371 S 3 38 2:35 1459 93 — S 4 392:42 1240 64 —

As shown in the table above, the set time and the stiffening time werecomparable between the control and inventive samples. Meanwhile, thenail pull strength, the core compressive strength, and the humidifiedbond were generally better for the gypsum wallboards made with sodiummonofluorophosphate.

Example 2

Gypsum boards were made with a formulation including stucco, water(i.e., water to stucco ratio of 0.9), foam, and ball mill accelerator.In these samples, the effect of the amount of sodium monofluorophosphate(e.g., about 1.5 g (0.21 wt. % based on stucco) and about 2.0 g (0.28wt. % based on stucco)) was investigated. The results are shown in thetable below:

Core Stiffening Set Board Compressive Sample time time Weight Nail PullStrength Description No. (s) (min:s) (lbs/MSF) (lb_(f)) (psi) 1.5 gSodium S 5 45 2:33 1297 79 — Monofluorophosphate S 6 42 2:28 1410 94 — S7 42 2:33 1324 81 389 S 8 44 2:50 1281 75 — S 9 42 2:30 1438 95 — 2.0 gSodium S 10 52 2:50 1345 87 — Monofluorophosphate S 11 56 2:52 1300 81 —S 12 58 3:05 1331 90 415 S 13 55 2:39 1373 94 — S 14 54 2:42 1308 87 — S15 53 2:33 1437 101 — S 16 51 2:50 1241 72 —

As shown in the table above, the stiffening times were generally longer(possibly indicating more fluidity) while the initial set times werecomparable to the control formulations of Example 1. Meanwhile,substantial increases in nail pull and compressive strength wereobserved when increasing the amount of sodium monofluorophosphate.

Example 3

Gypsum boards were made with a formulation including stucco, sodiummonofluorophosphate, starch, foam, and water (i.e., water to stuccoratio ranging from 0.74 to 0.9). Control boards were also made withoutsodium monofluorophosphate but instead with Plast-L. The results areshown in the table below:

Water Board Nail Sample Water/Stucco reduction Weight Na₂PO₃F Plast-LDispersant Pull No. Wt. Ratio (%) (lbs/MSF) (g) (g) (g) (lb_(f)) S 170.9 0 1373 2 0 0 94 S 18 1308 2 0 0 87 S 19 0.86 4.4 1399 2 0 0 88 S 200.8 11.1 1321 2 0 0 79 S 21 1279 2 0 0 69 S 22 0.77 14.4 1389 2 0 0 74 S23 0.74 17.8 1381 2 0 0 75 S 24 1335 2 0 0 63 S 25 0.7 22.2 1344 3 0 386 Control Boards with Plast-L CS 5 0.9 0 1337 0 1 0 75 CS 6 1278 0 1 066 CS 7 0.74 17.8 1383 0 1 0 60

As indicated in the table above, when using sodium monofluorophosphate,it allowed for a lower water to stucco ratio while providing a boardwith desirable properties. When using a dispersant, such aspolynaphthalene sulfonate in sample S 25, the reduction in water waseven further improved in comparison to a water/stucco weight ratio of0.9.

Example 4

Gypsum boards were made with a formulation including stucco, sodiummonofluorophosphate, retarder, dispersant, BMA, and water. Inparticular, a 20 wt. % solution of sodium monofluorophosphate was madeby adding 100 lbs of sodium monofluorophosphate to 400 lbs of water. Themixture was agitated for a few minutes and left undisturbed overnight.This solution was constantly agitated while feeding directly to theslurry mixer.

The line speed for the trial was 183 feet/minute. The other conditionsand changes made during the trial are listed in the table below. Thechanges indicated in the table below are cumulative. The first samplewas taken for the control at a time of 0 minutes.

Board Stiffening Time weight Nail Pull Slump Time Set Time (mins)(lbs/MSF) (lb_(f)) Changes (in) (s) (min:s) 0 1210 76 Control 7⅛ 38 2:456 1200 78 72 1230 74 Added 12.5 lbs/MSF of 8⅜ 70 3:13 75 1240 80 20%SMFP solution. 85 1220 74 Cut all retarder. 8½ 66 2:49 89 1190 74 93 —71 Cut all dispersant. 8¼ 69 3:19 99 1210 73 Cut BMA by 1 lb (16%) 1091210 76 Cut GW by 20 lbs (3%). 7¾ 57 3:08 115 1220 74

As soon as the sodium monofluorophosphate was added, the slump increasedby 1¼ inch while the stiffening time increased by 32 seconds and the settime increased by 28 seconds. Removing the retarder and dispersantappeared to show minimal effect on stiffening, slump, and/or the settime. Removal of the ground water reduced the slump to 7¾ inches, still⅝ inches greater than the control, while the stiffening and the set timewere 19 seconds and 23 seconds, respectively, longer than the control.This may suggest that even more water may be reduced. In general, thetrial provided evidence of the higher fluidity resulting from the use ofsodium monofluorophosphate.

Example 5

Gypsum boards were made with a formulation including stucco, sodiummonofluorophosphate, retarder, dispersant, BMA, and water. Inparticular, an 11 wt. % solution of sodium monofluorophosphate was madeby adding 100 lbs of sodium monofluorophosphate to 800 lbs of water. Themixture was agitated for approximately one hour and the solids werecompletely dissolved. This solution was constantly agitated whilefeeding directly to the slurry mixer.

The line speed for the trial was 210 feet/minute. The other conditionsand changes made during the trial are listed in the table below. Thechanges indicated in the table below are cumulative. The first samplewas taken for the control at a time of 0 minutes.

Board Stiffening Time weight Nail Pull Slump Time Set Time (mins)(lbs/MSF) (lb_(f)) Changes (in) (s) (min:s) 0 1230 75 Control 6⅞ 33 2:347 1230 78 101 1230 77 Added 20 lbs/MSF of ~11% 7 45 2:26 106 1220 74SMFP solution. Cut all retarder. Cut all dispersant. Added 2 lbs/MSF BMA(40%). Cut GW by 30 lbs/MSF (5%). 112 1230 81 Added 1 lb/MSF BMA (20%).7 34 2:18

These and other modifications and variations of the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims.

1. A slurry for making a gypsum board, the slurry comprising stucco,water, and a phosphorus containing compound comprising a phosphite, aphosphate having the formula P(O)_(n)(X)_(m) wherein n is from 0 to 4, mis from 0 to 6, the sum of n and m is from 3 to 6, and X is hydrogen,halogen, sulfur, or selenium, a salt thereof, or a mixture thereof. 2.The slurry of claim 1, wherein the phosphorus containing compoundcomprises a phosphite.
 3. The slurry of claim 1, wherein the phosphoruscontaining compound comprises a phosphate having the formulaP(O)_(n)(X)_(m) wherein n is from 0 to 4, m is from 0 to 6, the sum of nand m is from 3 to 6, and X is hydrogen, halogen, sulfur, or selenium, asalt thereof.
 4. The slurry of claim 3, wherein X includes fluoro. 5.The slurry of claim 3, wherein n is from 2 to
 3. 6. The slurry of claim3, wherein m is from 1 to
 2. 7. The slurry of claim 1, wherein thephosphorus containing compound comprises a halophosphate.
 8. The slurryof claim 1, wherein the phosphorus containing compound comprises amonohalophosphate.
 9. The slurry of claim 1, wherein the phosphoruscontaining compound comprises a salt including an alkali metal, analkaline earth metal, a transition metal, or a combination thereof. 10.The slurry of claim 1, wherein the phosphorus containing compoundcomprises sodium monofluorophosphate.
 11. The slurry of claim 1, whereinthe phosphorus containing compound is present in the slurry in an amountof from 0.01 wt. % to 5 wt. % based on the weight of the stucco.
 12. Theslurry of claim 1, wherein the weight ratio of the water to the stuccois from 0.1 to
 3. 13. The slurry of claim 1, wherein the slurry furthercomprises a dispersant.
 14. The slurry of claim 13, wherein thedispersant comprises a sulfonate, a polycarboxylate ether, apolycarboxylate ester, or a mixture thereof.
 15. The slurry of claim 1,wherein the gypsum slurry is characterized by having a set time of 3.5minutes or less using a ¼ pound Gillmore needle according to ASTM C266.16. A method for making a gypsum board, the method comprising depositingthe slurry of claim 1 on a first facing material, providing a secondfacing material on the slurry, and allowing the stucco to convert tocalcium sulfate dihydrate.
 17. A gypsum board made according to themethod of claim
 18. 18. A gypsum board comprising a gypsum corecomprising gypsum, and a phosphorus containing compound comprising aphosphite, a phosphate having the formula P(O)_(n)(X)_(m) wherein n isfrom 0 to 4, m is from 0 to 6, the sum of n and m is from 3 to 6, and Xis hydrogen, halogen, sulfur, or selenium, a salt thereof, or a mixturethereof.
 19. The gypsum board of claim 18, wherein the phosphoruscontaining compound comprises a salt.
 20. The gypsum board of claim 19,wherein the salt includes a monohalophosphate.
 21. The gypsum board ofclaim 19, wherein the salt includes an alkali metal, an alkaline earthmetal, a transition metal, or a combination thereof.
 22. The gypsumboard of claim 18, wherein the phosphorus containing compound comprisesfrom 0.001 lbs/MSF to 150 lbs/MSF of the board weight.
 23. The gypsumboard of claim 18, wherein the board exhibits a nail pull resistance of70 lb_(f) or more when measured according to ASTM C1396, a compressivestrength of 300 psi or more when measured according to ASTM C1396, orboth.